The long-term objective of this project is to further our knowledge of the many cell surface molecules on developing retinal axons and on one of their specific target tissues, the optic tectum. The retino-tectal map is highly ordered and is formed under the guidance of specific directional cues as well as other influences. Two-dimensional gel analyses of cell surface and extracellular proteins from these tissues reveal the existence of large numbers of proteins and protein families about which little is known. The initial approach of this project employed a strategy for generating monoclonal antibodies that was based on knowledge of receptors that mediate cell-cell interactions in the immune system. The assumption was made that molecules involved in specific axonal-axonal, axonal-tectal, and other interactions of importance in establishing pathways and directional cues ar likely to include proteins that are both very scarce and are expressed on the cell surface or in the extracellular matrix. The special procedures developed to generate monoclonal antibodies (MAbs) against such proteins have been remarkably successful even though only one of twelve size fractions of cell surface proteins has been studied to date. A large numbe of different MAbs were generated. These identify most cell surface protein in this size range that have been reported by other laboratories to play a role in neural embryogenesis. A large number of novel proteins were also identified. The staining patterns of these MAbs on appropriate tissues reveal two general classes of patterns. The first class stains all neurons in a given pathway as do molecules thought to play a more or less general role in cell adhesion, e.g., N-CAM or Ng-CAM. The second class, "Pattern MAbs," stains subsets of axons in previously undescribed patterns. One of these, called Pattern 5 (Pat 5), stains only a subset of the axons in the E retina, optic nerve and chiasm. A second, Pat 10, stains anterior ganglion cell fibers but fails to label fibers in a major region of the posterior retina. A third, Pattern Bravo, stains retinal axons in still another pattern. Bravo has already been sequenced and is a member of the immunoglobulin (IG) family of cell surface receptors. At least five different exons are alternatively spliced to generate considerable diversit among the products of the Bravo gene. Partial sequence from a clone of the Pat 10 cDNA has yielded evidence that it too is a member of the Ig supergen family, and Pat 5 exhibits gel migration behavior typical of molecules in I domains. The Ig family, together with the integrin and cadherin families, accounts for most of the molecules already known to play major cell recognition roles in the assembly of the nervous system. The primary focus of the next phase of this project will be on molecular studies of Bravo; Pat 5 and Pat 10.